This is something my mom is prone to repeating: it's a story about how some mother wanted her kid to be healthy, so she made him a tuna sandwich every day for lunch, and the kid ended up getting mercury poisoning from all the tuna.

What I want to know is, is there any truth to it? My mom is very prone to repeating stories she's heard without verifying them and thus passing along ULs, so I'd like to know if there are any documented cases of kids actually getting sick or dieing of mercury poisoning caused by eating canned tuna (which as far as I know has a much lower mercury content than fresh tuna).

From a quick google search it seems there's definitely a recommended cut off point for the amount of tuna people should eat per week depending on how much they weigh (here's an article with a handy chart) but other articles also point out that some people are more susceptible to mercury poisoning than others.

The bottom line is that too much tuna can result in too much mercury and you might end up with symptoms of mercury poisoning (loss of balance, etc).

Yeah, I've seen the medical warnings too, I'm just trying to find recorded instances. In large part because it's after 3 in the morning here and I'm supposed to stay awake all night, so I'm looking for things to keep me occupied.